Composite structures are typically constructed from multiple layers or plies. These plies may include a variety of materials such as carbon fiber, various other fibers, metal foils, and the like. In addition, the plies may be pre-impregnated with a resin and are often dispensed from a roll or spool. In roll form, the ply material is referred to as “tape” and typically includes a paper backing film. This backing film generally prevents pre-impregnated ply material (prepreg) from adhering to itself and aids in handling the ply as the ply is applied to the tool and the layup. In particular, at the beginning and end of each ply placement, the ply material is generally cut to match the profile of the layup while the backing film is left intact. In this manner, the intact backing film is utilized to guide the severed ply on to the layup. During the layup process, the backing film is removed prior to placement of any subsequent ply.
A disadvantage associated with conventional backing film material is that the backing film rips or tears. In particular, cuts in the backing film, introduced during the ply cutting procedure, often serve as a starting point for a tear. As the backing film is removed, torn backing film may remain on the ply, may foul the ply placement head, and/or may lead to breakage of the backing film.
Another disadvantage associated with conventional backing film is that it is usually a relatively thick calendered claycote type paper. The weight and thickness of this paper reduce the yardage of ply material that may be placed on a spool of a given diameter. Reducing the thickness of the conventional backing film in an effort to place more backed ply material on a spool, however, increases the tendency of the backing film to tear.
Yet another disadvantage associated with conventional backings films is the opaque nature of the paper. This opacity precludes visual inspection of the ply placement until the backing film is removed. Once the backing film is removed from the ply, the handling characteristics of the ply are negatively impacted so, it is difficult or impossible to adjust the ply placement.
Accordingly, it is desirable to provide a backing film for pre-impregnated ply material that is capable of overcoming the disadvantages described herein at least to some extent.